Differences in neurobehavioral responses of chinook salmon (Oncorhynchus tshawytscha) and rainbow trout (Oncorhynchus mykiss) exposed to copper and cobalt: Behavioral avoidance

Behavioral avoidance of copper (Cu), cobalt (Co), and a Cu and Co mixture i n soft water differed greatly between rainbow trout (Oncorhynchus mykiss) a nd chinook salmon (O. tshawytscha). Chinook salmon avoided at least 0.7 mu g Cu/L, 24 mu g Co/L, and the mixture of 1.0 mu g Cu/L and 0.9 mu g Co/L, w hereas rainbow trout avoided at least 1.6 mu g Cu/L, 180 mu g Co/L, and the mixture of 2.6 mu g Cu/L and 2.4 mu g Co/L. Chinook salmon were also more sensitive to the toxic effects of Cu in that they failed to avoid greater t han or equal to 44 mu g Cu/L, whereas rainbow trout failed to avoid greater than or equal to 180 mu g Cu/L. Furthermore, following acclimation to 2 mu g Cu/L, rainbow trout avoided 4 mu g Cu/L and preferred clean water, but c hinook salmon failed to avoid any Cu concentrations and did not prefer clea n water. The failure to avoid high concentrations of metals by both species suggests that the sensory mechanism responsible for avoidance responses wa s impaired. Exposure to Cu concentrations that were not avoided could resul t in lethality from prolonged Cu exposure or in impairment of sensory-depen dent behaviors that are essential for survival and reproduction.